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A virtual colonoscopy is used to identify signs of colorectal cancer. It also is used to locate polyps and growths of tissue in the colon and rectum, which may be precancerous. The procedure, also called computed tomographic (CT) colonography, uses a CT scan to construct images of these areas, which make up your large intestine. After the scan, a computer combines the images of the colon and rectum to produce both two- and three-dimensional interior views. In some cases, magnetic resonance imaging (MRI) is used instead of CT scanning.
The difference between virtual colonoscopy and conventional colonoscopy is how the images of your colon and rectum are retrieved. Conventional colonoscopy uses a colonoscope, which is a long, lighted tube. This flexible tube, which is placed inside your colon and rectum, uses a small camera to send images of the areas to a video monitor. Virtual colonoscopy uses a CT or MRI to take pictures of the inside of the colon from outside of your body.
Virtual colonoscopy is used for early detection of colon cancer in men and women. It allows a physician to look at your colon and rectum to find abnormal areas, which may indicate polyps or tumors. With early detection, some polyps can be found and removed before they can turn into cancer. If cancer is already present, it is more likely to be curable if it is found early.
The United States Preventive Services Task Force (USPSTF) recommends screening for colorectal cancer using fecal occult blood testing, sigmoidoscopy, or colonoscopy in adults, beginning at age 50 years and continuing until age 75. This is an A recommendation—in other words, there is a high certainty that net benefit is substantial. The USPSTF recommends against routine screening for colorectal cancer in adults age 76 to 85 years. The USPSTF do not include either CT colonography (CTC or so-called virtual colonoscopy) or DNA stool tests as screening tests, saying that there was not enough current evidence to judge the harms and benefits of the new technology.
The American Cancer Society recommends that men and women who do not have a family history of colon cancer or other high-risk factors start regular colorectal screenings at age 50. Screening every five years is advised for patients who have had a virtual colonoscopy. If you are at a high risk for colon cancer, you physician will set your screening schedule. High-risk factors include a family history of polyps or cancer, diabetes, obesity, Crohn’s disease, and ulcerative colitis.
To allow your physician to get the clearest images, your colon and rectum must be emptied before a virtual colonoscopy. This is called bowel prep.
Tell your physician about any medications you are taking at least one week before the exam in case any changes need to be made to your medication schedule.
A virtual colonoscopy is usually done in a hospital, but it is an outpatient procedure. This means that you will not be checked into the hospital and can leave again on the day of the test. It takes 10 to 15 minutes to complete and you will not be sedated. The testing process is as follows:
There are few risks associated with virtual colonoscopy. The air in your colon may make you feel bloated, but the feeling should dissipate once you pass the air from your body. Rarely, some patients have a negative reaction to the contrast agent. Though uncommon, mild reactions can include:
Moderate to severe responses to the contrast agent, though rare, resemble an allergic reaction and may include:
There is a very small risk that inflating your colon could cause injury. The American Cancer Society considers this risk to be much lower with virtual colonoscopy than conventional colonoscopy. Also, like other types of CT scan, this test subjects you to a small, but safe, amount of radiation.
After your virtual colonoscopy, a radiologist will review the CT or MRI images. If your physician is not satisfied with the images, you may need to repeat the scan or have another type of screening.
The results of a virtual colonoscopy are negative if there are no abnormalities in your colon. The results of the test are positive if any abnormalities or polyps are found. If your results are positive, your physician may recommend a conventional colonoscopy, during which abnormal tissue samples can be obtained and polyps can be removed.
Other abdominal problems not associated with colorectal cancer may also be found during virtual colonoscopy. Tumors in the abdomen or the areas surrounding the kidney, liver, pancreas, or spleen may be detected since these organs lie near your large intestine.
Written by: Anna Giorgi
Published on: Aug 07, 2012
Medically reviewed on: Mar 02, 2016: The Healthline Medical Review Team
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